The present invention relates to a shutter opening device for opening a shutter mounted on a disc cartridge, which includes a hard case and a disc-shaped information recording medium contained in the hard case, upon recording and reproducing information on the medium with a disc driving device.
A magnetic disc for use with a personal computer is generally classified into a 5.25 inch-diameter floppy disc and a 3.5 inch-diameter floppy disc. The 5.25 inch-diameter floppy disc is contained in a flexible case, which is formed with a head insertion opening for allowing insertion of a magnetic head therefrom and effecting writing or reading of signals. In contrast, the 3.5 inch-diameter floppy disc is contained in a disc cartridge case having a shutter for normally closing a head insertion opening, and when signals are written or read, the shutter must be opened to expose the head insertion opening and allow insertion of the magnetic head therefrom. Therefore, the disc driving device is provided with a shutter opening device.
FIG. 7 is a bottom plan view of a 3.5 inch-diameter floppy disc cartridge generally designated by reference numeral 1. Referring to FIG. 7, the disc cartridge 1 is basically comprised of a hard case 2 having a square shape as viewed in plan, a magnetic disc 3 rotatably contained in the case 2, and a shutter 4 mounted on a forward end portion of the case 2 with respect to an insert direction of the case 2 into the disc driving device as depicted by an arrow A, which shutter 4 is slidable in a direction (as depicted by an arrow B) perpendicular to the insert direction of the case 2.
FIGS. 8 and 9 are a perspective view of the shutter 4 and a cross section taken along the line C--C in FIG. 8, respectively. Referring to FIGS. 8 and 9, the shutter 4 has a substantially U-shaped configuration, and a bottom side portion of the shutter 4 to be opposed to a magnetic head mounted on the side of a carriage (not shown) upon loading of the disc cartridge 1 is formed with a pair of hinges 5a and 5b projecting inwardly. Referring back to FIG. 7, the case 2 is formed with a guide channel 6 on the bottom side to be engaged with the hinges 5a and 5b of the shutter 4 in such a manner that the hinges 5a and 5b can slide along the guide channel 6 in the direction B. Reference numeral 7 designates a pair of magnetic head insertion openings formed on the opposite sides of the case 2.
FIG. 10 is a plan view of a cartridge holder 8 for receiving the disc cartridge 1 and retaining the same therein. Referring to FIG. 10, there is provided an ejecting plate or lever member 9 at a right upper portion of the cartridge holder 8 as viewed in FIG. 10, that is, at a deepest portion of the cartridge holder 8 with respect to the insert direction A of the disc cartridge 1. The ejecting plate 9 functions to open the shutter 4 upon insertion of the disc cartridge 1 and push the disc cartridge 1 upon ejecting of the same. A tension coil spring 10 is engaged between a hook 17 of the ejecting plate 9 and a hook 18 of the cartridge holder 8 so that the ejecting plate 9 is elastically biased in a counterclockwise direction as viewed in FIG. 10 by the spring 10 and is rotatably supported by a pin 11. FIG. 10 shows an unloaded condition where the disc cartridge 1 is not inserted in the cartridge holder 8. When the disc cartridge 1 is inserted from a cartridge insert hole 12 of the disc cartridge 1, a contact portion E of the disc cartridge 1 as shown in FIG. 7 is brought into contact with a contact edge 13 of the ejecting plate 9. When the disc cartridge 1 is further inserted, the ejecting plate 9 is rotated clockwise as shown by an arrow F in FIG. 10 against the biasing force of the tension coil spring 10. Accordingly, the contact edge 13 of the ejecting plate 9 is moved leftwardly as viewed in FIG. 10 to thereby urge an end surface 16 of the shutter 4 and open the shutter 4.
Generally, a disc driving device having the above-mentioned cartridge holder 8 for use with the disc cartridge 1 is designed in such a manner that the disc cartridge 1 is horizontally loaded into the cartridge holder 8 irrespective of a horizontal condition or a vertical condition of the disc cartridge 1. Therefore, a force for opening the shutter 4 after contacting of the disc cartridge 1 with the ejecting plate 9 is caused by either of a pushing force from an operator or a drawing force to be generated by an auto-loading mechanism provided in the disc driving device. However, there has been developed another type disc driving device as designated by reference numeral 14 in FIG. 11 such that the disc cartridge 1 is inserted vertically downwardly. In this type disc driving device 14, the disc cartridge 1 is obliged to fall freely at the initial stage of insertion, causing impact of the contact portion E of the disc cartridge 1 against the contact edge 13 of the ejecting plate 9. As a result, the shutter 4 of the disc cartridge 1 is brought into disengagement from the case 2 as shown in FIGS. 12 and 13. FIG. 12 is a top plan view of the disc cartridge 1, and FIG. 13 is a bottom plan view of the disc cartridge 1. Referring to FIG. 14 which shows an essential part of the disc cartridge 1 in perspective, a supporting portion 15 of the case for supporting the hinge 5a of the shutter 4 is formed in a cantilever fashion. Although such a cantilever structure contributes to simple and convenient mounting of the shutter 4, it is considered that when an unintended excess force is applied to the shutter 4 in a disengaging direction thereof, the supporting portion 15 will be flexed to cause disengagement of the hinge 5a.
FIG. 15 is an enlarged plan view illustrating the relationship between the ejecting plate 9 and the shutter 4 when the contact edge 13 of the ejecting plate 9 comes into abutment against the end surface 16 of the shutter 4 to open the shutter 4. There will now be studied a force F to be applied to the hinge 5a by impact insertion of the disc cartridge 1 into the cartridge holder of the disc driving device with reference to FIG. 15. Referring to FIG. 15, reference character b denotes a distance between both the hinges 5a and 5b; reference character a denotes an arm length between an abutment point 13a of the contact edge 13 and the hinges 5a and 5b; reference character l denotes a distance between the center of the right hinge 5b and the end surface 16 of the shutter 4; reference character f.sub.1 denotes a force to be applied to the shutter 4 by a clockwise moment of the ejecting plate 9 upon impact insertion of the disc cartridge 1; and reference character f.sub.2 denotes an anti-frictional force to be generated by a reaction of an elastic force normally applied to the shutter 4 in its closing direction.
In this case, a force F.sub.1 to be applied to the hinge 5a due to the force f.sub.1 is expressed as follows: EQU F.sub.1 =(f.sub.1 .times.a)/b
Further, a force F.sub.2 to be applied to the hinge 5a due to the force f.sub.2 is expressed as follows: EQU F.sub.2 =(f.sub.2 .times.l)/b
Accordingly, the resultant force F to be applied to the hinge 5a is expressed as follows: EQU F=F.sub.1 +F.sub.2
This force F is applied in a direction as shown by an arrow .beta. coinciding with the shutter insert direction. If the resultant force F exceeds an elastic limit of the supporting portion 15 of the case, the supporting portion 15 is elastically deformed to cause the disengagement of the hinge 5a from the guide channel 6 as shown in FIGS. 12 and 13, resulting in an unusable condition of the disc cartridge 1. The elastic limit as mentioned above is about 200 gf at a low value. In some case, when the disc cartridge is let freely fall from a height of about 7 cm to abut against the contact edge 13 of the ejecting plate 9, the hinge 5a of the shutter 4 comes into disengagement. In this case, the contact edge 13 of the shutter 4 first abuts against the contact portion E of the case 2, and then impulsively abuts against the end surface 16 of the shutter 4.
To prevent the disengagement of the hinge 5a, it is considered to form the ejecting plate 9 into a shape such that the contact edge 13 first abuts against the shutter 4. However, there is generated a force resisting insertion of the shutter 4 in a direction counter to that of the force f.sub.2 shown in FIG. 15, causing the generation of a frictional force due to this resisting force to result in a possibility of the shutter 4 being unopened.